In the past, ignition systems used cam driven breaker points which would supply 12 volt pulses to an ignition coil. This system suffered from the lack of high voltage at high engine revolutions. Additionally the spark plugs would not burn off the carbon on the electrodes. As the carbon built up on the electrodes, the spark plug would begin to fail. Improvements on this system included capacitive discharge circuits which increase the output potential of the ignition coil. The capacitive discharge and conventional breaker points ignition systems would produce a uniform spreading of combustion within the engine cylinders. However, it has been found that up to 15% of the time, the ignition spark would be blown out. As such the mixture within the cylinders would not ignite and would be exhausted. This of course decreased the engine efficiency.
It has been shown that the problems of spark plug misfirings and ignition spark blowouts can be substantially overcome by producing a high voltage ignition pulse having a frequency between approximately 7 KHZ to 14 KHZ. Typical patents showing this technique are U.S. Pat. Nos. 3,260,299 to Lister, 3,305,108 to Kaehni and 4,131,100 to Merrick.
Some of the problems encountered with the audio frequency ignition systems included, a drop off of voltage at high speeds, instability of the spark frequency as the engine RPM changed and high maintenance cost due to engine heat and vibration. Additionally, many of the prior systems were of a highly complex nature which substantially increased the production costs of the ignition systems.